It is known that 1,4-.beta.-N-acetylmuramidases are enzymes capable of selectively cleaving the glycosidic bond between N-acetylglucosamine and N-acetylmuramic in the peptidoglycans which form the cell wall of bacteria. This wall is thus lysed, thereby entailing the death of the cells. These enzymes, more commonly called lysozymes, thus act as bactericides, and this property explains their generalized presence in most of the biological fluids of higher animals. Lysozyme is indeed found, at various levels of concentration, in blood, tears, saliva, milk, etc., of mammals. It is also found in the vegetable kingdom, e.g. in papaya. However, industrial-scale extraction of lysozymes is carried out from egg white, where it is present in relatively great concentration, by various absorption and/or precipitation processes. For example, see Belgian patent No. 694,538.
Present applications of chicken lysozymes are mostly in the pharmaceutical area, where it is used to fight various infections. Other applications are in the food industry. For instance, it is known that lysozyme can be used in the manufacture of baked pressed-paste cheese to efficiently inhibit during ripening the development of butyric acid bacteria responsible for manufacturing defects including cheese blowing. For example, see French patent No. 8,003,321. It can also be used for the preservation of various perishable foodstuffs, such as meat products (A. Akashi, Jap. J. Zootechnical Sci. 42, 1971, 289); wines (Japanese patent No. 3115/71, 1971); or sake (M. Yajima et al., J. Ferm. Technol. 46, 1968, 782). It can further be used to preserve milk components for pediatric use (Japanese patent 16780/70, 1970).
These various applications represent a considerable potential market insofar as lysozyme can be produced easily, in large amounts and at a sufficiently low cost. The various processes presently enabling extraction of lysozyme from egg white are commercially acceptable only if the egg white can be reused in food after being treated. Lysozyme production capacity is therefore partly ruled by the egg white market, and this poses a problem more difficult to solve in that technical difficulties, and even in some countries legal restraints, limit the use of treated egg white in standard foodstuffs.
These problems, which are linked to the availability of natural sources of lysozyme, become insurmountable in the case of mammalian lysozymes, whether the initial concentration thereof is too low, as with cow milk lysozyme, or the raw material is practically unavailable, as with human lysozyme. Thus it appears that there is a need for a technique enabling production of lysozyme and avoiding the hereabove described problems.